Interleukin-4 (IL-4) and IL-4delta2 mRNA gastric expression was evaluated in healthy subjects and patients who did not have ulcers but were infected with Helicobacter pylori with or without the cag pathogenicity island (cag PAI). IL-4 mRNA was physiologically expressed by gastric epithelium and negatively influenced by H. pylori. Also, nonepithelial cells in the lamina propria of H. pylori-infected patients expressed IL-4 mRNA, whereas IL-4delta2 mRNA was found only in cag PAI-negative patients. Thus, gastric IL-4 takes part in the local immune response to H. pylori.